1. Field of the Invention
The present invention relates to an automatic development method of, for example, photosensitive lithographic printing plate and an automatic development device thereof. In particular, the invention relates to a technology for controlling a fluctuation of the sensitivity of a developer against changes of the development processing condition in the minimum level.
2. Description of the Related Art
In general, in an automatic development device of photosensitive lithographic printing plate, a replenishing system due to aging and due to processing in which a development replenisher is replenished in a developing tank where a developer is stored, a plate area of a lithographic printing plate to be processed is measured, and the development replenisher is replenished in an amount corresponding to the measured value (this system will be hereinafter referred to as “area-based replenishing system due to aging”) is employed as a measure for managing the sensitivity of the developer.
However, in such an area-based replenishing system due to aging, a high-precision plate area measurement device of lithographic printing plate is required in a development processing section of the automatic development device, and therefore, there was a problem of complication of the structure and an increase of the costs. Also, it is difficult to distinguish whether the photosensitive side of the lithographic printing plate is a single side or double sides (hereinafter referred to as “single side/double sides”) and to distinguish the plate type (such as a plate having a different coating amount of the photosensitive layer). For these reasons, there was encountered such a problem that if a necessary replenishing amount of the development replenisher changes due to the changes of the plate area, single side/double sides and plate type of the lithographic printing plate, it becomes difficult to adequately achieve the replenishment of the development replenishing amount.
Then, so far, as described in, for example, Japanese Patent No. 2,516,022 (JP-A-64-21451), a replenishing system in which an electric conductivity of a developer is measured, the measured value is compared with an electric conductivity value exhibiting an optimum sensitivity as previously experimentally determined (this electric conductivity value will be hereinafter referred to as “adequate electric conductivity value”), and when the measured value is lower than the adequate electric conductivity value, a development replenisher is replenished (this system will be hereinafter referred to as “electric conductivity-based replenishing system”) was employed as a method of replenishing a development replenisher of an automatic development device for photosensitive lithographic printing plate. In such an electric conductivity-based replenishing system, even if the plate area, single side/double sides and plate type of the lithographic printing plate to be processed change, it is possible to replenish an adequate amount of the development replenisher, thereby keeping the sensitivity of the developer adequate.
However, in general, there is an empirical fact that the adequate electric conductivity value is different between a developer which has fatigued only by carbon dioxide gas due to aging and a developer which has fatigued only by plate processing (in the case of silicate based treating agent, fatigue due to aging (fatigue by carbon dioxide gas)—recovery by replenishment: 65 mS/cm, fatigue by processing—recovery by replenishment: 55 mS/cm; and in the case of non-silicate based treating agent, fatigue due to aging—recovery by replenishment: 56 mS/cm, fatigue by processing—recovery by replenishment: 39 mS/cm;). For this reason, in the foregoing electric conductivity-based replenishing system, in the case where the processing frequency, for example, the daily processing amount, is different from an expected value, a rate of the actual replenishing amount due to aging to the actual replenishing amount due to processing is also different from an expected value. Therefore, there is encountered such a problem that an adequate electric conductivity value of the whole of the developer in a developing tank calculated from the respective adequate electric conductivities changes and a difference from the preset adequate electric conductivity value is generated, whereby it becomes impossible to adequately keep the sensitivity of the developer.
On the other hand, JP-A-9-96910 proposes an automatic developing device in which a time interval for replenishment is measured, a necessary replenishing amount due to aging is determined within that time interval, by considering a value obtained by subtracting this replenishing amount due to aging from the replenishing amount per unit time as a replenishing amount due to processing, the replenishing amount due to processing and the replenishing amount due to aging are respectively determined, and the electric conductivity of developer is controlled by the electric conductivity value calculated from a proportion of the resulting replenishing amount due to processing and replenishing amount due to aging. According to this measure, even if the plate area, single side/double sides and plate type of the lithographic printing plate to be processed change, by estimating a proportion of the replenishing amount due to processing to the replenishing amount due to aging, it is possible to deduce an adequate electric conductivity value of developer.
However, according to the foregoing method of controlling the electric conductivity of developer by the electric conductivity value determined from a proportion of the replenishing amount due to processing to the replenishing amount due to aging as calculated from the time interval for replenishment, in the case where the fatigue condition due to aging is different, there is encountered such a problem that a precise proportion of the replenishing amount due to processing to the replenishing amount due to aging cannot be determined. Examples of the case where the fatigue condition due to aging is different include the case where the concentration of carbon dioxide gas in the circumferential atmosphere changes and the case where the wind velocity in the circumferential atmosphere changes. It is known that with respect to the former, the subject proportion changes depending upon the number of workers in a room where the automatic developing device is placed; and that with respect to the latter, the subject proportion changes depending upon the position of an air port or the air volume of an air conditioner. That is, according to the foregoing replenishing method, the previously experimentally determined replenishing amount due to aging in every unit time is different from the actual replenishing amount due to aging in every unit time depending upon increase or decrease of the number of workers in a room or the state of an air conditioner so that a precise replenishing amount due to aging cannot be determined from the time interval for replenishment. Thus, there is fear that a wrong target electric conductivity value is calculated.